/*******************************************************************************
 * Copyright (c) 2011 MadRobot.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the GNU Lesser Public License v2.1
 * which accompanies this distribution, and is available at
 * http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
 * 
 * Contributors:
 *  Elton Kent - initial API and implementation
 ******************************************************************************/
package com.madrobot.text;

/**
 * <p>
 * <code>StopWatch</code> provides a convenient API for timings.
 * </p>
 * 
 * <p>
 * To start the watch, call {@link #start()}. At this point you can:
 * </p>
 * <ul>
 * <li>{@link #split()} the watch to get the time whilst the watch continues in
 * the background. {@link #unsplit()} will remove the effect of the split. At
 * this point, these three options are available again.</li>
 * <li>{@link #suspend()} the watch to pause it. {@link #resume()} allows the
 * watch to continue. Any time between the suspend and resume will not be
 * counted in the total. At this point, these three options are available again.
 * </li>
 * <li>{@link #stop()} the watch to complete the timing session.</li>
 * </ul>
 * 
 * <p>
 * It is intended that the output methods {@link #toString()} and
 * {@link #getTime()} should only be called after stop, split or suspend,
 * however a suitable result will be returned at other points.
 * </p>
 * 
 * <p>
 * NOTE: As from v2.1, the methods protect against inappropriate calls. Thus you
 * cannot now call stop before start, resume before suspend or unsplit before
 * split.
 * </p>
 * 
 * <p>
 * 1. split(), suspend(), or stop() cannot be invoked twice<br />
 * 2. unsplit() may only be called if the watch has been split()<br />
 * 3. resume() may only be called if the watch has been suspend()<br />
 * 4. start() cannot be called twice without calling reset()
 * </p>
 * 
 * <p>
 * This class is not thread-safe
 * </p>
 * 
 */
public class StopWatch {

	private static final long NANO_2_MILLIS = 1000000L;

	// running states
	private static final int STATE_UNSTARTED = 0;

	private static final int STATE_RUNNING = 1;

	private static final int STATE_STOPPED = 2;

	private static final int STATE_SUSPENDED = 3;

	// split state
	private static final int STATE_UNSPLIT = 10;

	private static final int STATE_SPLIT = 11;

	/**
	 * The current running state of the StopWatch.
	 */
	private int runningState = STATE_UNSTARTED;

	/**
	 * Whether the stopwatch has a split time recorded.
	 */
	private int splitState = STATE_UNSPLIT;

	/**
	 * The start time.
	 */
	private long startTime;

	/**
	 * The start time in Millis - nanoTime is only for elapsed time so we
	 * need to also store the currentTimeMillis to maintain the old
	 * getStartTime API.
	 */
	private long startTimeMillis;

	/**
	 * The stop time.
	 */
	private long stopTime;

	/**
	 * <p>
	 * Constructor.
	 * </p>
	 */
	public StopWatch() {
		super();
	}

	/**
	 * <p>
	 * Start the stopwatch.
	 * </p>
	 * 
	 * <p>
	 * This method starts a new timing session, clearing any previous values.
	 * </p>
	 * 
	 * @throws IllegalStateException
	 *             if the StopWatch is already running.
	 */
	public void start() {
		if(this.runningState == STATE_STOPPED){
			throw new IllegalStateException("Stopwatch must be reset before being restarted. ");
		}
		if(this.runningState != STATE_UNSTARTED){
			throw new IllegalStateException("Stopwatch already started. ");
		}
		this.startTime = System.nanoTime();
		this.startTimeMillis = System.currentTimeMillis();
		this.runningState = STATE_RUNNING;
	}

	/**
	 * <p>
	 * Stop the stopwatch.
	 * </p>
	 * 
	 * <p>
	 * This method ends a new timing session, allowing the time to be retrieved.
	 * </p>
	 * 
	 * @throws IllegalStateException
	 *             if the StopWatch is not running.
	 */
	public void stop() {
		if(this.runningState != STATE_RUNNING && this.runningState != STATE_SUSPENDED){
			throw new IllegalStateException("Stopwatch is not running. ");
		}
		if(this.runningState == STATE_RUNNING){
			this.stopTime = System.nanoTime();
		}
		this.runningState = STATE_STOPPED;
	}

	/**
	 * <p>
	 * Resets the stopwatch. Stops it if need be.
	 * </p>
	 * 
	 * <p>
	 * This method clears the internal values to allow the object to be reused.
	 * </p>
	 */
	public void reset() {
		this.runningState = STATE_UNSTARTED;
		this.splitState = STATE_UNSPLIT;
	}

	/**
	 * <p>
	 * Split the time.
	 * </p>
	 * 
	 * <p>
	 * This method sets the stop time of the watch to allow a time to be
	 * extracted. The start time is unaffected, enabling {@link #unsplit()} to
	 * continue the timing from the original start point.
	 * </p>
	 * 
	 * @throws IllegalStateException
	 *             if the StopWatch is not running.
	 */
	public void split() {
		if(this.runningState != STATE_RUNNING){
			throw new IllegalStateException("Stopwatch is not running. ");
		}
		this.stopTime = System.nanoTime();
		this.splitState = STATE_SPLIT;
	}

	/**
	 * <p>
	 * Remove a split.
	 * </p>
	 * 
	 * <p>
	 * This method clears the stop time. The start time is unaffected, enabling
	 * timing from the original start point to continue.
	 * </p>
	 * 
	 * @throws IllegalStateException
	 *             if the StopWatch has not been split.
	 */
	public void unsplit() {
		if(this.splitState != STATE_SPLIT){
			throw new IllegalStateException("Stopwatch has not been split. ");
		}
		this.splitState = STATE_UNSPLIT;
	}

	/**
	 * <p>
	 * Suspend the stopwatch for later resumption.
	 * </p>
	 * 
	 * <p>
	 * This method suspends the watch until it is resumed. The watch will not
	 * include time between the suspend and resume calls in the total time.
	 * </p>
	 * 
	 * @throws IllegalStateException
	 *             if the StopWatch is not currently running.
	 */
	public void suspend() {
		if(this.runningState != STATE_RUNNING){
			throw new IllegalStateException("Stopwatch must be running to suspend. ");
		}
		this.stopTime = System.nanoTime();
		this.runningState = STATE_SUSPENDED;
	}

	/**
	 * <p>
	 * Resume the stopwatch after a suspend.
	 * </p>
	 * 
	 * <p>
	 * This method resumes the watch after it was suspended. The watch will not
	 * include time between the suspend and resume calls in the total time.
	 * </p>
	 * 
	 * @throws IllegalStateException
	 *             if the StopWatch has not been suspended.
	 */
	public void resume() {
		if(this.runningState != STATE_SUSPENDED){
			throw new IllegalStateException("Stopwatch must be suspended to resume. ");
		}
		this.startTime += (System.nanoTime() - this.stopTime);
		this.runningState = STATE_RUNNING;
	}

	/**
	 * <p>
	 * Get the time on the stopwatch.
	 * </p>
	 * 
	 * <p>
	 * This is either the time between the start and the moment this method is
	 * called, or the amount of time between start and stop.
	 * </p>
	 * 
	 * @return the time in milliseconds
	 */
	public long getTime() {
		return getNanoTime() / NANO_2_MILLIS;
	}

	/**
	 * <p>
	 * Get the time on the stopwatch in nanoseconds.
	 * </p>
	 * 
	 * <p>
	 * This is either the time between the start and the moment this method is
	 * called, or the amount of time between start and stop.
	 * </p>
	 * 
	 * @return the time in nanoseconds
	 */
	public long getNanoTime() {
		if(this.runningState == STATE_STOPPED || this.runningState == STATE_SUSPENDED){
			return this.stopTime - this.startTime;
		} else if(this.runningState == STATE_UNSTARTED){
			return 0;
		} else if(this.runningState == STATE_RUNNING){
			return System.nanoTime() - this.startTime;
		}
		throw new RuntimeException("Illegal running state has occured. ");
	}

	/**
	 * <p>
	 * Get the split time on the stopwatch.
	 * </p>
	 * 
	 * <p>
	 * This is the time between start and latest split.
	 * </p>
	 * 
	 * @return the split time in milliseconds
	 * 
	 * @throws IllegalStateException
	 *             if the StopWatch has not yet been split.
	 */
	public long getSplitTime() {
		return getSplitNanoTime() / NANO_2_MILLIS;
	}

	/**
	 * <p>
	 * Get the split time on the stopwatch in nanoseconds.
	 * </p>
	 * 
	 * <p>
	 * This is the time between start and latest split.
	 * </p>
	 * 
	 * @return the split time in nanoseconds
	 * 
	 * @throws IllegalStateException
	 *             if the StopWatch has not yet been split.
	 */
	public long getSplitNanoTime() {
		if(this.splitState != STATE_SPLIT){
			throw new IllegalStateException("Stopwatch must be split to get the split time. ");
		}
		return this.stopTime - this.startTime;
	}

	/**
	 * Returns the time this stopwatch was started.
	 * 
	 * @return the time this stopwatch was started
	 * @throws IllegalStateException
	 *             if this StopWatch has not been started
	 */
	public long getStartTime() {
		if(this.runningState == STATE_UNSTARTED){
			throw new IllegalStateException("Stopwatch has not been started");
		}
		// System.nanoTime is for elapsed time
		return this.startTimeMillis;
	}

	/**
	 * <p>
	 * Gets a summary of the time that the stopwatch recorded as a string.
	 * </p>
	 * 
	 * <p>
	 * The format used is ISO8601-like,
	 * <i>hours</i>:<i>minutes</i>:<i>seconds</i>.<i>milliseconds</i>.
	 * </p>
	 * 
	 * @return the time as a String
	 */
	@Override
	public String toString() {
		return DurationFormatUtils.formatDurationHMS(getTime());
	}

	/**
	 * <p>
	 * Gets a summary of the split time that the stopwatch recorded as a string.
	 * </p>
	 * 
	 * <p>
	 * The format used is ISO8601-like,
	 * <i>hours</i>:<i>minutes</i>:<i>seconds</i>.<i>milliseconds</i>.
	 * </p>
	 * 
	 * @return the split time as a String
	 */
	public String toSplitString() {
		return DurationFormatUtils.formatDurationHMS(getSplitTime());
	}

}
